My dear Sir:

I had the honor of receiving your very pleasant letter of April 13th, inviting me to pay you a visit, but imagine my disappointment at not receiving it until my return from England a few days since—¹ While in London during April last, I decided not to use Dr. Gray’s letter of introduction to you, hearing that the state of your health prevented your seeing strangers, and was thus afraid that I should be encroaching on your limited time given to personal friends—²

Had not some strange mishap befallen your letter, I could have arranged to delay my return home and gone to see you— as it was I had but a few hours to spend in London on my return from Norway to take the Boston steamer—

Thanking you for your exceedingly kind invitation, and trusting that you may have the health & strength to complete to your full satisfaction the splendid series of works, to which I feel so much indebted as revolutionizing science, I remain, My dear Sir | with great esteem | Very truly & respectfully Yrs | A. S. Packard jr

Charles Darwin Esq. | &c &c.